Purpose :
Retinal inhibition is vital for shaping visual signals to highlight important aspects of the visual scene and may play an important role in retinal adaptation to increased background luminance. We previously showed that light adaptation reduced spontaneous inhibitory activity and the spatial extent of inhibition to OFF bipolar cells (BC). Dopamine release is the main neuromodulator of light adaptation and can modulate GABA receptors on retinal neurons. However, the contribution of dopamine to changes in BC inhibition due to light adaption has not been studied. To investigate this, spontaneous and light-evoked spatial inhibitory inputs were measured from OFFBCs in the mouse retina under different background luminance conditions and while either stimulating or blocking dopamine D1 receptors that are located on inner retinal neurons.

Methods :
Whole-cell voltage clamp was used to record light-evoked and spontaneous inhibitory postsynaptic currents from dark-adapted mouse OFFBCs, identified via fluorescent labeling. A white OLED screen was used to set the background light and to generate 25 μm bars of light flashed for 1 sec to map spatial inhibition. D1 receptors were activated with SKF 38393 (SKF, 20 µM) and blocked with SCH 23398 (SCH, 50 µM). The charge transfer and peak amplitude of light-evoked responses and the peak amplitude and frequency of spontaneous events were measured. The spatial distributions were averaged and compared between conditions.

Conclusions :
These data show that dopamine signaling through D1 receptors plays a prominent role in modulation of inner retinal inhibition to OFFBCs. Modulation of spontaneous inhibition by light adaptation could be completely mimicked by activation of D1 receptors, but there are likely other important factors that contribute to the narrowing of OFF bipolar surround receptive fields seen with light-adaptation.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.